Air springs for railroad cars of this type have been known, as disclosed in Patent Document 1 and Patent Document 2. These springs are designed to include an elastic mechanism having a laminated rubber structure and integrally attached under an air spring part, so that the railroad car can exhibit a favorable suspension performance with these two types of springs combined and arranged in series.
The rubber and a lower support that form the elastic mechanism are usually joined together by bonding (such as vulcanized adhesion or by adhesive). To achieve a favorable bonding strength between the rubber and the lower support, as is known, an end of the rubber in contact with the lower support is enlarged in diameter toward the lower support so as to have a widen end shape (i.e., enlarged toward the end), as shown in Patent Document 3 (Suspension device for railroad cars). This technique is also used in other technical fields than air springs for railroad cars, for example as shown in Patent Document 4 (Seismic isolation device).
As load conditions and the like for air springs for railroad cars are more and more stringent, a problem that the end of an elastic member in the elastic mechanism tends to easily separate from the lower support has emerged. The elastic member such as rubber may have an end processed to have a structure in which the elastic member is downward enlarged with a smooth concave curve surface and connected to the lower support (see FIG. 2), a structure in which the lower end of the elastic member at the outer peripheral edge has a certain thickness in the vertical direction (see FIG. 4), or a two-stage downward enlarged structure with an upper, first concave curve surface and a lower, second concave curve surface (see FIG. 3). There is a problem wherein the detachment or separation of the lower end of the elastic member can readily occur from the outer periphery in any of the elastic mechanisms having these structures.
The rubber member (as one example of an elastic material) in the elastic mechanism is usually made by molding with the use of the lower support. Rubber is poured onto the lower support that is coated with adhesive in advance. It has been found out that the coat of adhesive flows away with the in-flowing rubber in the vulcanization process of rubber (when the elastic material is poured in), so that there is very little or almost no adhesive left at ends, because of which separation would easily occur at the ends. This problem occurs similarly with other elastic materials than rubber such as synthetic resin having elasticity.